Bond heads for thermocompression bonders, thermocompression bonders, and methods of operating the same

ABSTRACT

A bond head for a thermocompression bonder is provided. The bond head includes a tool configured to hold a workpiece to be bonded, a heater configured to heat the workpiece to be bonded, and a chamber proximate the heater. The chamber is configured to receive a cooling fluid for cooling the heater.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.14/746,065, filed Jun. 22, 2015, which is a continuation of U.S. patentapplication Ser. No. 14/314,149, filed Jun. 25, 2014, which claims thebenefit of U.S. Provisional Application No. 61/842,081, filed Jul. 2,2013, the contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to semiconductor bonding machines, andmore particularly, to improved bond head assemblies for bonding machinesfor forming electrical interconnections.

BACKGROUND OF THE INVENTION

The present invention relates to bonding machines and has particularapplicability to thermocompression bonding machines and bondingtherewith.

Thermocompression bonding machines are be used in bonding a plurality ofconductive regions on one substrate to a plurality of conductive regionson another substrate. For example, such bonding machines may be used tobond a semiconductor die (e.g., including conductive regions such asbumps or pillars formed on the die) to another substrate (e.g., wherethe another substrate may be another die, a wafer, a leadframe, or anyother substrate used in packaging). In certain exemplarythermocompression bonding machines, a placer tool (also referred to as aplace tool, a placing tool, a bonding tool, or simply a tool to hold orbond a workpiece) is used to bond the one substrate (e.g., a die, alsoreferred to as a workpiece) to the another substrate. In connection withthe bonding of the die/workpiece, it may be desirable to heat thedie/workpiece, for example, to heat the conductive regions on thedie/workpiece.

According to the present invention, novel structures and methods areprovided which permit heating of a bonding tool (carrying a workpiecesuch as a die) to allow proper bonding of the workpiece to an underlyingsubstrate, and then a controlled and rapid cool down of the heater (andthus the bonding tool) before transfer of another workpiece onto thebonding tool to again repeat the cycle.

SUMMARY OF THE INVENTION

According to an exemplary embodiment of the present invention, a bondhead for a thermocompression bonder comprises a tool configured to holda workpiece to be bonded, a heater configured to heat the workpiece tobe bonded, and a chamber proximate the heater, the chamber configured toreceive a cooling fluid for cooling the heater.

According to another exemplary embodiment of the present invention, athermocompression bonder comprises a workpiece supply station includinga plurality of workpieces, a bonding station, a placer tool forreceiving a workpiece from the workpiece supply station and for bondingthe workpiece to a substrate at the bonding station, and a coolingstation for cooling the placer tool after bonding the workpiece to thesubstrate.

According to another exemplary embodiment of the present invention, athermocompression bonder comprises a bond head including (a) a toolconfigured to hold a workpiece to be bonded, (b) a heater configured toheat the workpiece to be bonded, and (c) a chamber proximate the heater,the chamber configured to receive a cooling fluid for cooling theheater.

According to another exemplary embodiment of the present invention, athermocompression bonder comprises a bond head including (a) a toolconfigured to hold a workpiece to be bonded, (b) a heater configured toheat the workpiece to be bonded, and (c) a chamber proximate the heater,the chamber configured to receive a cooling fluid for cooling theheater, the chamber adapted to move between a first position in contactwith the heater and a second position out of contact with the heater.

According to another exemplary embodiment of the present invention, athermocompression bonder comprises a bond head including (a) a toolconfigured to hold a workpiece to be bonded, (b) a heater configured toheat the workpiece to be bonded, and (c) a chamber proximate the heater,the chamber configured to receive a cooling fluid during a firstoperational phase, and a second fluid during a second operational phase.

According to another exemplary embodiment of the present invention, athermocompression bonder comprises a bond head including (a) a toolconfigured to hold a workpiece to be bonded, (b) a heater configured toheat the workpiece to be bonded, (c) a chamber proximate the heater, thechamber configured to receive a cooling fluid for cooling the heater,(d) a support structure above the heater, and (e) at least two flexuresdisposed between the support structure and the heater.

According to another exemplary embodiment of the present invention, amethod of thermocompressively bonding a workpiece to a substratecomprises the steps of (1) bonding a workpiece to a substrate using abond head of a thermocompression bonder, the bond head including aheater and (2) providing a cooling fluid into a chamber of the bond headproximate the heater to reduce a temperature of the heater after step(1).

Additional exemplary methods are disclosed herein, such as methods ofoperating any of the bond heads or bonding machines disclosed or claimedherein.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed descriptionwhen read in connection with the accompanying drawing. It is emphasizedthat, according to common practice, the various features of the drawingare not to scale. On the contrary, the dimensions of the variousfeatures are arbitrarily deformed or reduced for clarity. Included inthe drawing are the following figures:

FIG. 1 is a block diagram side view of elements of a conventionalthermocompression bonder;

FIGS. 2A-2D are block diagram views of bonding structures on a lowersubstrate, bonding structures on an upper substrate, and a conventionalmethod of bonding the upper substrate to the lower substrate;

FIG. 3A is a block diagram side view of a bond head assembly inaccordance with an exemplary embodiment of the present invention;

FIG. 3B is a detailed view of a first example lower bond head for thebond head assembly of FIG. 3A in accordance with an exemplary embodimentof the present invention;

FIG. 3C is a detailed view of a second example lower bond head for thebond head assembly of FIG. 3A in accordance with another exemplaryembodiment of the present invention;

FIGS. 3D-3E are block diagrams illustrating a chamber of a bond headassembly having a fluid therein, in accordance with an exemplaryembodiment of the present invention;

FIG. 4 is block diagram illustrating recirculation of a cooling liquidfluid through a chamber of a bond head assembly in accordance with anexemplary embodiment of the present invention;

FIGS. 5A-5B illustrate a chamber being moved in and out of contact witha heater of a bond head assembly in accordance with an exemplaryembodiment of the present invention;

FIGS. 6A-6C illustrate bond head assemblies including flexures inaccordance with various exemplary embodiments of the present invention;and

FIG. 7 is a block diagram illustrating operations of elements of abonding machine in accordance with an exemplary embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

According to certain exemplary embodiments of the present invention, abond head for a thermocompression bonder (e.g., a die attach bonder) isprovided which performs, for example, a local reflow solder attachprocess. A bonding tool of the bond head places and bonds a firstworkpiece (e.g., a die, an interposer, etc.) to a second workpiece(e.g., a substrate, a chip, a wafer, etc.) by melting and re-solidifyingof solder bumps on the workpiece (e.g., die) being placed. Typically,the bonding tool is in contact with the workpiece being placed duringthe entire heating cycle (and possibly the cooling cycle), making thetemperature ramp up and ramp down using a serial process affectingmachine throughput (e.g., units per hour, UPH). Therefore, it istypically desirable to achieve the temperature ramp up and ramp down inthe shortest possible time. A challenge is to quickly switch from aheating phase (where a minimal heat loss out of the bonding tool istypically desired) to a cooling phase (where a maximum heat loss out ofthe bonding tool is typically desired). In accordance with the presentinvention, bond head structures/assemblies (e.g., for solder die attach)for rapidly switching from a relatively low cooling rate to a muchhigher cooling rate are provided. For example, a cooling heat sink(e.g., a cooling chamber) is mechanically separated from the heated toolholder during heating, and then brought into contact during cooling.This combines a very low heat transfer into the heat sink duringheating, with a very high heat loss into the heat sink during cooling,effectively increasing the speed at which the bonding process can beperformed. Since the bonding times are typically several seconds, anytime savings is a direct benefit to total machine UPH.

In other exemplary embodiments of the present invention, a cooling heatsink (e.g., a cooling chamber which may be a low thermal mass, highthermal conductive structure) is attached directly to the non-processside of the heater (a side away from the tool which holds the workpieceto be placed). This structure may be filled with different fluidsdepending upon the present portion of the process. For example, whencooling is desired a cooling fluid will be circulated though the coolingheat sink to remove heat from the heater. During the temperature ramp upsegment of the process the cooling heat sink may be purged (e.g., usingair) to minimize the effective thermal mass of the heat sink which mustbe heated during the temperature ramp up segment of the process. Such anexemplary configuration combines a very low heat transfer out of theheat sink during heating with a very high heat loss from the heat sinkduring cooling, effectively increasing the speed at which the bondingprocess can be performed.

In other exemplary embodiments of the present invention, a bond headstructure is provided that allows for the bonding tool to rapidly heatand cool (where the temperature shift may be hundreds of degreesCelsius) while maintaining a desirable degree of precision positioningof the workpiece to be placed (e.g., die placement to single digitmicron or smaller levels). For example, a heater, tool (that holds theworkpiece), and the workpiece itself (e.g., a die) are supported on aflexure system whose primary compliance is designed to be radiallysymmetric from the center of the workpiece. For example, floating screwsmay pierce portions of the heater and facilitate movement of the heaterand flexures during heating, and cooling. Such a configuration may beused to constrain motion of the heater, tool and workpiece to beradially symmetric about the center of the workpiece. This providescompliance to allow for differential expansion to occur in a desirableand predictable fashion.

In thermocompression bonding, it is often desirable to heat the tool ofthe placer while holding the workpiece to be bonded (e.g., during thebonding process—which may be considered a non-cooling phase)—but it isalso desirable to have the tool of the placer at a lower temperatureduring other operational phases (e.g., a cooling phase) of the processsuch as during (1) the picking (or transfer) of another workpiece to thetool from a workpiece supply (e.g., a wafer), and/or (2) during initialplacing of the workpiece before the high temperature bonding. Inaccordance with various exemplary embodiments of the present invention,chambers are provided as part of the bond head (also referred to as abond head assembly), where a cooling fluid may be provided in thechamber. In certain embodiments, two different fluids may be used insuch a chamber (e.g., a liquid cooling fluid during the cooling phase,and a fluid such as air during a non-cooling phase). In otherembodiments, the chamber (which may use one or more fluids, as desired)may be moved in and out of contact with the heater, or a force betweenthe chamber and heater may be varied.

FIG. 1 is a block diagram side view of elements of thermocompressionbonder 100. Die 102 is to be bonded to substrate 104 using placer 106(including a bond tool) as illustrated in FIG. 1. Placer 106 holds die102, and substrate 104 is supported by bond stage 110. Camera 114 isshown interposed between placer 106 and bond stage 110 (but could be inother locations), and has split field vision, that is it images bothupwardly, towards die 102, and downwardly, towards substrate 104. Ofcourse, other positions and configurations of a camera may be used.Using appropriate mechanisms and visual information provided by camera114, placer 106 (and/or bond stage 110) is repositioned as necessary toalign bonding structures on die 102 with corresponding bondingstructures on substrate 104 (see below). Camera 114 is moved so thatplacer 106 with aligned die 102 may be lowered over substrate 104, anddie 102 is bonded to substrate 104. The bonded die 102/substrate 104structure is indexed, or moved, to output indexer 112 with intermediateelements, not shown but represented by double headed arrow 118. Then,another substrate 104 is taken from input indexer 108, with intermediateelements, not shown but represented by double headed arrow 116, andplaced on bond stage 110, and placer 106 takes another die 102 from, forexample, a semiconductor wafer or another structure having indexed die102. Another die 102 is aligned with another substrate 104, usinginformation from repositioned and interposed camera 114, and the processrepeats. Of course, many different or additional elements may beincluded in thermocompression bonder 100, and as such it is understoodthat the present invention is not limited to integration with theillustrated exemplary configuration of FIG. 1.

The present invention relates to bonding of a first workpiece to anotherworkpiece. The term “substrate” is interchangeably used with the term“workpiece”. The workpieces/substrates described herein may be, forexample, semiconductor dice, wafers, leadframe devices, interposers(e.g., silicon, glass, etc.), amongst others. In one specific exampleillustrated herein, the workpiece being bonded by the bond head is asemiconductor die and the substrate to which the semiconductor die isbeing bonded is a substrate. The conductive regions (also referred to asbonding structures) on each workpiece may be, for example, conductivepillars (e.g., Cu pillars), metalized pads, amongst others.

FIGS. 2A-2D illustrate details of bonding structures on lower substrate204, bonding structures on upper substrate 202 (e.g., a die 202), andthe method of bonding die 202 to substrate 204. Specifically, asillustrated in FIG. 2A substrate 204 has bonding structures 228 that maybe, for example, copper (Cu) structures 228, such as copper pillars ormetallized pads, grown on substrate 204 that collectively form a targetconductive region. As shown, optional plating layer 220 may cover Custructures 228 to facilitate bonding. Plating layer 220 may comprise,for example, solder (e.g., tin (Sn)-based solder) or other materials tofacilitate bonding. FIG. 2B illustrates Cu structures 228 and substrate204 covered with a non-conductive paste (NCP) layer 222. For example,NCP layer 222 may be an encapsulant material marketed by Henkel AG & Co.A non-conductive film (NCF) (not shown) may be provided over uppersubstrate 202, that is, over pillars 224 and overlying layer 226. As isknown to those skilled in the art, pillars 224 tend to push through suchan NCF (not shown) during bonding of pillars 224 to correspondingstructures 228.

NCP layer 222 may be an adhesive type encapsulant material that may besubstantially planar as illustrated. As illustrated in FIG. 2C,die/substrate 202 includes a series of pillars 224 (only one is shown)comprised of, for example, copper (Cu), aluminum (Al), gold (Au), etc.Cu pillars 224 may include an overlying layer 226 of, for example,solder, such as tin-based solder, to facilitate bonding between die Cupillars 224 with lower substrate Cu structures 228. While FIG. 2C onlyillustrates one Cu pillar 224 aligned with a corresponding Cu structure228, die 202 may comprise many Cu pillars 224 that are each aligned witha lower Cu structure 228. It is noted that Cu structures 228 on lowersubstrate 204 may be elongated structures, which is they may extendalong a Y-axis that goes in and out of the paper of FIG. 2C. Regardless,die 202 is lowered such that solder tipped Cu pillar(s) 224 contact, andpress into NCP layer 222. When solder tipped Cu pillar(s) 224 engagecorresponding plated Cu structures 228, pressure and heat is appliedsuch that Cu pillar(s) 224 are bonded to Cu structure(s) 228 asillustrated in FIG. 2D. In effect Cu pillar solder layer 226merges/combines with substrate Cu structure plating layer 220 to forminterface 229 between Cu pillar 224 and Cu structure 228. NCP layer 222,and any NCF film on the upper substrate 202, may be comprised of athermal setting material that cures with temperature, so they are keptbelow a critical temperature, for example below 180° C., as Cu pillars224 push through NCP layer 222. NCP and NCF may serve to assist inbinding, or fixing, bonded die 202 and substrate 204. Die 202 with Cupillars 224 are heated before/during bonding as will be illustrated inthe drawings and described below.

FIG. 3A illustrates bond head 306 a (which is included in a placersystem, similar to the placer 106 shown in FIG. 1, except that bond head306 a includes aspects of the present invention described below). Bondhead 306 a includes Z-motor 332, theta Z-drive 334, tilt head controlmechanism 336, and lower bond head 330. Certain aspects of bond head 306a (including Z-motor 332, theta Z-drive 334, and tilt head controlmechanism 336) may be found on the iStack^(PS)™ die bonder sold byKulicke & Soffa Pte Ltd. Tilt head control mechanism 336 may permittilting of lower bond head 330 in either, or both of, X- and Y-axes (seeXYZ legend 338 with the Z-axis up/down, the X-axis to the right/left andthe Y-axis coming into and out of the paper of FIG. 3A).

FIG. 3B illustrates a more detailed view of lower bond head 330 of FIG.3A, and includes interface tilt lower bond head 340, support structure(e.g., distribution and insulation block) 342, chamber 344, heater 348,tool 350 and die 302 held by tool 350. Interface tilt lower bond head340 may include a load cell that measures Z-axis force (downward,bonding force), and optionally may provide for direct Z-forcemeasurement and feedback during bonding of the force applied to die 302.Support structure 342 may represent and include, for example, electricalconnections, air connections, water connections, and insulation toisolate lower heater 348. As will be discussed below in greater detail,heater 348 heats tool 350 which heats die 302 before and/or duringbonding (e.g., see FIG. 2C-2D). Chamber 344 regulates the temperature,or amount of heat, of heater 348 before, during, and/or after bonding(e.g., assists in ensuring NCP layer 222 shown in FIGS. 2B-2D does notcure prematurely from too high a temperature of die 302/tool 350) andserves to cool heater 348 (and thus tool 350 and die 302) atpredetermined points in the bonding cycle. A cooling fluid is broughtthrough chamber 344 using piping or tubing 346 a, 346 b, with pipe 346 abeing the inlet pipe and pipe 346 b the outlet pipe. Cooling fluid maybe brought into chamber 344 during a cooling phase (e.g., after bondingof a workpiece) for cooling of heater 348 from one temperature to alower predetermined temperature (e.g., a predetermined temperature). Thecooling fluid absorbs the heat from heater 348, cooling heater 348 andraising the temperature of the cooling fluid and the higher temperaturecooling fluid exits chamber 344 through outlet 346 b. FIG. 3Cillustrates another embodiment where chamber, heater and tool areintegrated into a single structure, chamber/heater/tool structure 352where the functions are substantially the same. In another example, theheater and tool are integrated into a single structure, with a distinctchamber (where the chamber may take any of the forms disclosed orclaimed herein). In yet another example, the chamber and heater areintegrated into a single structure, with a distinct tool.

FIG. 3D illustrates chamber 344 filled with a gas, such as air (“fluid2”), and FIG. 3E illustrates chamber 344 filled with another fluid(e.g., a liquid cooling fluid) (“fluid 1”), having a thermal capacitygreater than fluid 2 as fluid 1 is the cooling fluid to cool heater 348.In either respect, fluid 1 is capable of removing heat from heater 348by conduction (direct contact between the cooling fluid chamber/chamber344 and heater 348 (or integrated heater of FIG. 3C)), convection(through any air or gas between the cooling fluid chamber/chamber 344and heater 348 without direct contact), or heat transfer mechanisms.Fluid 2, such as a gas (e.g., air) may have a lower thermal capacitythan fluid 1 (such as a liquid having a greater thermal capacity). Thatis, a cooling liquid fluid would typically require greater energy toraise the temperature of a set volume of cooling liquid fluid than forthe equivalent volume of cooling gas fluid, for example. It iscontemplated that a fluid 2 gas could be sufficiently cooled, supercooled, etc., to increase or vary its thermal capacity.

Examples of fluid 2, in gas form, include: air filtered to 0.01 μm; airdirectly from factory supply lines; etc. Examples of fluid 1, in liquidform, include: water; distilled water; distilled water with a corrosiveinhibitor added; ethylene glycol (i.e., automotive antifreeze);non-conductive fluids such fluorinated liquids; etc. Examples of thecorrosive inhibitors (that may be added to, e.g., distilled water) areZalman™ G200 BLUE™ (available from Acoustic PC (www.acoustic.com)); RedLine Water Wetter® available from Redline Synthetic Oil Corporation ofBenicia, Calif.; and Valvoline® Zerex® coolant available from Ashland,Inc. of Covington, Ky. Examples of fluorinated liquids are: 3M®Fluorinert® electronic liquids marketed by the 3M Company of St. Paul,Minn.; and Galden® PFPE high performance, inert fluorinated liquidsmarketed by Solvay Plastics (www.solvayplastics.com).

FIG. 4 is a block diagram of recirculation of a cooling liquid fluid(e.g., fluid 1) through chamber 444 which may by used in connection withthe structure of FIGS. 3A-3E, where chamber 444 replaces chamber 344/352(or other exemplary embodiments of the present invention illustratedand/or described herein). As illustrated a cooling liquid fluid may besupplied by fluid tank 460 to chamber 444 when valve 474 is open. Thecooling liquid enters chamber 444, travels through chamber 444 (where itmay, or may not, cool a heater or the like (not shown)) and exits. The(warmed/heated) cooling liquid passes through check valve 462 (explainedin greater detail below) and into cooling liquid reservoir 464. Fluidpump 466 pumps the fluid 1 through the system and pumps the heatedcooling liquid from cooling liquid reservoir 464 to radiator 468.Radiator 468 permits the heat/excess heat from the heated cooling liquidfluid to be removed by, for example, radiator action, to bring thetemperature of the cooling liquid to an acceptable level. The cooledliquid fluid then returns to liquid tank 460 through pipe 472, as atarrow 478 and may recirculate though the system. Fluid 2 (e.g., air) isprovided from tank 470, and may be used to replace, remove, or blow out,cooling liquid fluid from chamber 444. During this process, liquid valve474 is closed and air/gas valve 476 is opened. The air is pumped intochamber 444 and displaces the cooling liquid, with the cooling fluidexiting chamber 444 through check valve 462. When the air displaces asufficient amount of the cooling liquid in chamber 444, the air exitschamber 444 and into check valve 462. An air exhaust valve (e.g., ableeder valve) may be provided somewhere in the system (e.g., somewherebetween or proximate elements 462, 464, 466, and 468) to remove, orbleed off, any air left in the system. It is noted that the elements andconfiguration shown in FIG. 4 is exemplary in nature, and may bereplaced by different or additional elements (e.g., a different coolingstructure may be used as opposed to radiator 468).

FIGS. 5A-5B illustrate bond head 530 in accordance with an alternateexemplary embodiment of the present invention. Specifically, cavity 580is defined by support structure 542 and is sized and positioned toaccept chamber 544 therein with sufficient room to permit chamber 544 tomove upwardly and downwardly within cavity 580. Z-actuator 582 moveschamber 544 along the Z-axis, so as to bring chamber 544 into, and outof, contact with heater 548 to facilitate cooling of heater 548. Asillustrated, interface tilt lower bond head 540 is over supportstructure 542. Support structure 542 includes cavity 580 within whichchamber 544 (and inlet and outlet pipes 546 a, 546 b) may be movedupwardly, away from underlying heater 548, and downwardly to contactheater 548. Inlet pipe 546 a brings cooling fluid to chamber 544 andoutlet pipe 546 b allows removal of (heated) cooling fluid from chamber544. Tool 500 is below heater 548 and holds die 502. In operation,(e.g., see as FIG. 5B) when heater 548 is to be cooled, chamber 544,with cooling fluid that may be recirculating through chamber 544 (e.g.,see FIG. 4), is lowered using Z-actuator 582 to contact heater 548 toabsorb heat from heater 548 through, for example, conduction. Cooledrecirculating cooling fluid enters chamber 544 through inlet pipe 546 a,absorbs heat from heater 548, and heated cooling fluid exits chamber 544through outlet pipe 546 b to be cooled and recirculated (e.g., see FIG.4).

FIGS. 5A-5B illustrate chamber 544 being moved in and out of contactwith heater 548. In an alternative embodiment, where the elements (e.g.,chamber 544 and heater 548) remain in contact, a contact force betweenchamber 544 and heater 548 may be varied in order to change the heattransfer therebetween.

FIGS. 6A-6C illustrate bond heads 630, 630 a, 630 b in accordance withexemplary embodiments of the present invention with flexures. In FIG.6A, interface structure 640 is over support structure 642. Linkage 690and flexures 692 a, 692 b are interposed between support structure 642and heater 648. Heater 648 retains tool 600 which in turn carries die602. During thermocompression bonding, the device holding die 602, forexample, tool 600, must be rapidly heated from about 130-150° C. toabout 250-300° C. in a minimum amount of time to enable acceptablethroughput, that is, a rate of bonding a plurality of die 602 to atarget conductive region (e.g., see FIGS. 2A-2D). During bonding, thebonder is required to hold die 602 in position within, for example, 5 μmin any direction. However, the thermal coefficient of expansion of thematerial comprising heater 648 should be taken into account. Forexample, aluminum nitride (with which heater 648 may be made from) has acoefficient of expansion of about 4.3 μm/m. For a typical die size of 10mm by 10 mm, an aluminum nitride heater may expand upwards of 7 μm for a170° C. temperature rise (from 130° C. to 300° C.) which may cause thedie shift outside of an allowed tolerance band, and produce faultyproduct. To mitigate this phenomenon, flexures 692 a, 692 b areinterposed between heater 648 and support structure 642 of the diebonder. While flexures are illustrated as spring members that expandalong the z-axis, this is a simplified illustration.

Specifically, flexures 692 a, 692 b are anisotropically flexible, thatis flexures 692 a, 692 b are most compliant along a line (and possiblyalong a vector) that is substantially parallel to the holding surface ofthe tool, and in a direction from a center of the holding surface of thetool outwards toward the flexures. Stated differently, flexures 692 a,692 b are compliant along the X-axis and Y-axis (e.g., see legend inFIG. 6A) in a direction from a center of the holding surface of the tooloutwards toward the flexures.

Flexures 692 a, 692 b may desirably be positioned in a radial patternbetween support structure 642 and heater 648, where any number offlexures may be used (only two flexures are illustrated in FIGS. 6A-6Cfor simplicity). It is desirable that the flexures be configured suchthat the line/vector of least stiffness points in a direction from thecenter of the tool to the respective flexure. Each flexure may desirablybe designed such that it has the same contribution in resisting thethermal growth of heater 648 as each other flexure. While undergoingthermal growth this will result in a virtual point at the center of thetool to undergo no in-plane motion.

In practice, flexures 692 a, 692 b may pierce heater 648 using floatingscrews or the like (not shown). This permits heater 648 to expandlaterally (i.e., radially about the virtual center point of the heater),with flexures 692 a, 692 b guiding the expansion during a heating cyclewhile keeping a point in the virtual center of the heater from any X-Yin-plane motion. During a cooling cycle, flexures 692 a, 692 b guide, orencourage, heater 648/tool 600 to return to it/their initial position,centered about, for example, the tool, during the contraction of theheater. This novel construction defines the growth point of the tool,and ensures that the growth point is predictable.

FIG. 6A illustrates an exemplary embodiment that includes linkage 690also interposed between heater 648 and support structure 642. Linkage690 may include, for example, some form of cooling to cool heater 648 asdiscussed above, and may also include electrical connections, airconnections, water connections, cooling fluid connections and insulationto isolate heater 648 (e.g., see support structure 642) from otherportions of the bond head. Regardless, linkage 690 may serve to coolheater during predetermined portions of a bonding cycle. Flexures 692 a,692 b, also interposed between support structure 642 and heater 648oppose lateral expansion (thermal growth) of heater 648 during rapidheating of heater 648 during bonding, and maintains die 602 within apredetermine tolerance position, and return flexures 692 a, 692 b guidedie 602 back to its centered position (see above).

FIG. 6B illustrates another exemplary embodiment similar to that of FIG.6A but with external inlet and outlet pipes/lines 646 a, 646 b supplyingcooled cooling fluid into linkage 690 and removing heated cooling fluidfrom linkage 690. Linkage 690 may also include electrical connections,air connections, and water connections. Flexures 692 a, 692 b aresimilar to those illustrated in FIG. 6A as to location and function.

FIG. 6C illustrates a further exemplary flexure embodiment similar tothat of FIG. 6B but with cooling chamber 694 positioned within cavity680 formed in support structure 642 (e.g., see FIGS. 5A-5B). Linkage 690and flexures 692 a, 692 b are interposed between support structure 642and heater 648. External inlet and outlet pipes/tubing 646 a, 646 bserve to introduce cooled cooling fluid into cooling chamber 694 andremove heated cooling fluid from cooling chamber 694, respectively.Cooling chamber 694 is configured to move within cavity 680 along atleast the Z-axis using Z-actuator 682. For example, after bonding die602 to an underlying substrate, cooling chamber may be moved downwardlyand brought into direct contact with linkage 690, the (cooled) coolingfluid removes heat from linkage 690, to cool, or lower the temperatureof, linkage 690. In turn, heater 648 is cooled by contact withcooling/cooled linkage 690, and then tool 600 is cooled by contact withcooling/cooled heater 648. When the cooling process is complete, coolingchamber is moved upwardly using Z-actuator 692 and cooling fluid maystill circulate through cooling chamber 694.

For example, in these exemplary flexure embodiments, flexures 692 a, 692b may be placed in an equidistant radial pattern about linkage 690 andbetween support structure 642 and heater 648. Such a spacing may ensurethat a center point of heater 648 remains fixed relative to linkage 690,with no in-plane motion so that die 602 has minimal, or no, movement dueto the thermal expansion of heater 648 (e.g., see the above discussionfor FIGS. 6A-6C). While two flexures 692 a, 692 b are illustrated inFIGS. 6A-6C, any number may be used, for example, 3, 4, 5, 6, etc.,preferably in a radial pattern. It is also contemplated that theflexures may take the form of a unitary anisotropically flexible annularflexure structure (not shown), or portions of an otherwiseanisotropically flexible annular flexure structure. Such an annularflexure structure may also include recirculating cooling fluid tomaintain its temperature/reduce its temperature and/or reduce thetemperature of heater 648. Flexures may maintain their positions on theheater by friction. Further, the flexures are anisotropically flexiblein that they are flexible substantially along a line/vector to a holdingsurface of a bonding tool (or perpendicular to a longitudinal axis alongthe length of the bonding tool) used to bond the die (workpiece) to thesubstrate.

In accordance with certain exemplary embodiments of the presentinvention described above, a cooling chamber is described for contactinga heater and removing heat therefrom (e.g., see FIGS. 3A-3E, FIGS.5A-5B, etc.). According to a further exemplary embodiment of the presentinvention, the tool (e.g., tool 350 of FIG. 3B) may be moved to anintermediate cooling stage after bonding a workpiece (e.g., a die) andbefore picking another such workpiece to be bonded. In such anarrangement (see FIG. 7), the tool may be brought into contact (or atleast proximate) a cooling stage to remove heat from the tool. Thiscooling arrangement may be provided as a replacement for, or in additionto, the various cooling configurations described herein (e.g., includinga chamber with a cooling fluid).

FIG. 7 illustrates placer 706 (including a tool, not shown) for holdingand bonding a workpiece 702 (e.g., die 702) to an underlying substrate704 supported by bond stage 710. In FIG. 7, die 702 has already beenbonded to substrate 704. Placer 706 is then moved from bond stage 710 tocooling stage 754 that is included as part of (or provided proximate to)the thermocompression bonder. Placer 706 is brought into contact with(or at least proximate) cooling stage 754 where heat from placer 706 isabsorbed or otherwise removed. For example, a tool (not shown) of placer706 may be brought into contact with a cooling pad of cooling stage 754,thereby reducing the temperature of placer 706 (i.e., reducing thetemperature of the relevant portion of placer 706 such as the tool andheater, not shown). Cooled placer 706 is then removed from cooling stage754 and moved to workpiece supply 756 (e.g., a wafer) to obtain anotherworkpiece (e.g., to pick another die from a wafer).

As provided above, an intermediate cooling stage (such as stage 754shown in FIG. 7) may be provided as an alternative to, or in additionto, cooling from a chamber as described in the various embodimentsabove. FIG. 7 also illustrates two temperature versus time curves. Curve1 relates to use of an intermediate cooling stage without an integratedcooling chamber, while curve 2 relates to an arrangement including anintegrated chamber cooling (e.g., as in FIGS. 3A-3E) plus use of anintermediate cooling stage. Referring to curve 1, after leaving bondstage 710 the temperature curve is substantially flat (see area A₁) asthere is no intentional cooling. When placer 706 reaches cooling stage754 the temperature drops rapidly as shown at area B₁ until thetemperature normalizes at area C₁. Referring to curve 2, after leavingbond stage 710 the temperature curve is decreasing continuously due tothe chamber cooling (see area A₂). When placer 706 reaches cooling stage754 the temperature drops rapidly as shown at area B₂ until thetemperature normalizes at area C₂. The normalized temperature (at areasC₁ and C₂) may be below the critical temperature of NCP and/or NCFlayers (e.g., see FIG. 2C).

While certain exemplary devices are illustrated and described herein, itis contemplated that other cooling chambers may have differingstructures, means, and methods of cooling. For example, a coolingchamber may be provided sufficiently large to accept at least a heater,with the cooling chamber acting as a deep freezer to rapidly cool down apost-bond heater with or without direct contact.

Other alternatives that may be used to vary the heat transfer betweenthe heater and any of the chambers described herein are contemplated.For example, a flow rate of a cooling fluid (e.g., such as the liquidcooling fluids described herein) may be varied depending upon thedesired heat transfer and/or depending upon the portion of the bondingprocess (or other operational phases during non-bonding).

Although the invention is illustrated and described herein withreference to specific embodiments, the invention is not intended to belimited to the details shown. Rather, various modifications may be madein the details within the scope and range of equivalents of the claimsand without departing from the invention.

What is claimed is:
 1. A method of thermocompressively bonding aworkpiece to a substrate, the method comprising the steps of: (a)bonding a workpiece to a substrate using a bond head of athermocompression bonder, the bond head including a heater; and (b)providing a cooling fluid into a chamber of the bond head proximate theheater to reduce a temperature of the heater after step (a), wherein thechamber is adapted to move within a cavity defined by the bond headbetween a first position in contact with the heater and a secondposition out of contact with the heater.
 2. The method of claim 1further including the step of providing the chamber in contact with theheater during step (a).
 3. The method of claim 1 further including thestep of applying a force between the chamber and the heater during steps(a) and (b).
 4. The method of claim 3 wherein the force applied duringstep (b) is different from the force applied during step (a).
 5. Themethod of claim 1 wherein a heat exchange takes place between the heaterand the chamber during step (b).
 6. The method of claim 1 wherein thecooling fluid is provided into the chamber at step (b) and a secondfluid is provided into the chamber after step (b).
 7. The method ofclaim 6 wherein a liquid is provided as the cooling fluid into thechamber in step (b), and a gas is provided into the chamber after step(b).
 8. The method of claim 1 further including a step of disposing atleast two flexures between a support structure of the bond head and theheater.
 9. The method of claim 8 wherein the at least two flexures eachare anisotropically flexible.
 10. The method of claim 8 wherein each ofthe at least two flexures are anisotropically flexible such that each ofthe flexures are compliant along a line that is substantially parallelto a holding surface of the tool, and in a direction from a center ofthe holding surface of the tool outwards toward the respective flexure.11. The method of claim 8 wherein each of the at least two flexures aremost flexible along a respective line originating in a center of theheater and extending toward the respective flexure.
 12. A method ofthermocompressively bonding a workpiece to a substrate, the methodcomprising the steps of: (a) bonding a workpiece to a substrate using abond head of a thermocompression bonder, the bond head including (i) atheta Z-drive mechanism, (ii) a lower bond head, and (iii) a tilt headcontrol mechanism positioned between the theta Z-drive mechanism and thelower bond head, the lower bond head including a heater; and (b)providing a cooling fluid into a chamber of the lower bond headproximate the heater to reduce a temperature of the heater after step(a).
 13. The method of claim 12 further including the step of providingthe chamber in contact with the heater during step (a).
 14. The methodof claim 12 further including the step of applying a force between thechamber and the heater during steps (a) and (b).
 15. The method of claim14 wherein the force applied during step (b) is different from the forceapplied during step (a).
 16. The method of claim 12 wherein a heatexchange takes place between the heater and the chamber during step (b).17. The method of claim 12 wherein the cooling fluid is provided intothe chamber at step (b) and a second fluid is provided into the chamberafter step (b).
 18. The method of claim 17 wherein a liquid is providedas the cooling fluid into the chamber in step (b), and a gas is providedinto the chamber after step (b).
 19. The method of claim 12 furtherincluding a step of disposing at least two flexures between a supportstructure of the bond head and the heater.
 20. The method of claim 19wherein the at least two flexures each are anisotropically flexible. 21.The method of claim 19 wherein each of the at least two flexures areanisotropically flexible such that each of the flexures are compliantalong a line that is substantially parallel to a holding surface of thetool, and in a direction from a center of the holding surface of thetool outwards toward the respective flexure.
 22. The method of claim 19wherein each of the at least two flexures are most flexible along arespective line originating in a center of the heater and extendingtoward the respective flexure.